1. Field of the Invention
This invention relates to a method of producing colored images on various substrates. By first coating the substrate with a sealer and when dried, coating with a water based pigmented photo-sensitive coating; after drying, exposing this coating to ultraviolet light through a photographic negative, and developing this image by removing the unexposed portion with water. These colored images using this process are particularly useful in preparing direct images, transfer or rub off images, and can also be used in preparing pre-press proofs that more closely resemble actual press proofs or press runs than similar proofs from the techniques of the prior art.
2. Description of the Prior Art
The color printing industry is, of course, massively large, with billions of dollars going toward the creation of beautiful color reproductions of photographs for magazines, art work, sales brochures, and the like.
As a color print job is laid out, it is often necessary to prepare a color proof or composition for careful examination prior to going forward with the substantial expense of setting up the press for commercial printing of the color reproduction. The original art work might consist of a single negative or multi negatives for complex color work, or it might consist of accurate four color separations to reproduce process color images.
A disadvantage of the prior art process is that most direct imaging and transfer systems use solvent based ink solutions which contain flammable or hazardous materials. In addition, a clear solvent solution or solutions which are also flammable or hazardous must be used for these images to be developed after exposure to ultraviolet light.
When using the method which uses a solvent based ink, another disadvantage is that the system will not hold fine line detail which is necessary in many cases of reproductions of art work and mandatory when required to make a detailed four color process image.
In Lupo, U.S. Pat. No. 2,716,061, a pigmented contact printing emulsion is disclosed for use in reproducing multi-colored photographic images on flexible supports, and especially vinyl plastic sheets. While having some similarity to the invention of this application, the formulations disclosed in the Lupo patent exhibit significant disadvantages, and are not practically capable for commercial use in the preparation of direct imaging, transfer lettering or, pre-press proofs.
Substantial disadvantages are found in the commercially available formulation of the Lupo patent compared with the preferred formulations of this invention. First, the formulation of the Lupo patent is less viscous and when a substrate is coated by placing it in a conventional whirler it dries unevenly and leaves mottled areas having different color densities. Furthermore, the exposed coating of the prior art patent tends to wash away more easily than the exposed coating in accordance with this invention after a comparable amount of exposure to ultraviolet light. The Lupo method also uses a washing step involving abrasives and an ink which comprises casein which shortens the ink's shelf life.
The photosensitive emulsion or varnish of this invention requires less ultraviolet light exposure time to cure. Further, the exposed photosensitive coating of this invention may be washed with pure water to remove the non-cross-linked portions, rather than requiring an ammonium hydroxide solution for washing as in the prior art. Additionally the use of casein is not necessary, thus giving the ink of this invention an increased shelf life.
In Thompson, U.S. Pat. No. 4,737,436, a method of making color proofs of images is disclosed for use in high image resolution color photomechanical imaging. The method disclosed in the Thompson patent also exhibits significant disadvantages. One disadvantage involves the blending of pigments to produce a pigment of predetermined color. The color of a pigment, being a dried powder, generally is not the same as the color of the pigment dispersed in a vehicle, and thus, it is difficult to obtain true colors using the method of the Thompson patent. Another disadvantage is the requirement of the use of a nitrocellulose sealer, which is flammable and poses toxicological hazards to both person and property. Another disadvantage is the use of a diazo sensitizer which, when used in a proper manner, has a very short life time of approximately 10-20 days and does not have an extended shelf life.
The ink color of this invention is produced by blending dispersed pigments in the ink solution, rather than by blending dry pigment, resulting in a more true to life ink color. Further, due to the large number of nitrocellulose-based sealer coats commercially available, it may be difficult to select a coat which is most compatible with the desired ink formulation. The unique nitrocellulose-based sealer coat disclosed herein is formulated to be compatible with the ink formulation disclosed herein and the unique property of this coating is produced by the acid and the plasticizer which give it the necessary adhesion, flexibility and flow properties not only when applied to a substrate but also when the ink of this invention is applied over it. Additionally, this invention discloses a unique water-based sealer coat, which is compatible with the ink formulation disclosed herein, which is a suitable alternative to nitrocellulose-based sealer coats.
In Kreiter, U.S. Pat. No. 4,710,447, a method and ink solution used for producing color proofs is disclosed which uses a powder coat which acts as a matting layer or bonding agent for the ink solution. The powder coat is applied to the sealer coat so as to dull the sealer finish and make the ink solution more adherent to the sealer coat. This powder coat is a disadvantage in that first, it requires an extra step and extra ingredient in the method, thus increasing complexity. Second, a specific sealer must be selected which creates a coat compatible with the selected powder coat. An additional disadvantage of the Kreiter patent is the ink formulation which will not lay down on the sealer coat without the use of the powder coat.
The ink formulation of this invention is compatible with both the known nitrocellulose-based sealer coats and the water-based sealer coat disclosed herein without the need for a powder coat, or any additional matting or adhering agent. The lack of need of such additional coats or agents reduces the complexity of both the color proofing process and the physical structure of the color proof of this invention when compared to the prior art. Further, the ink formulation of this invention will lay down on known nitrocellulose-based sealer coats and the water-based sealer coat disclosed herein.
The prior art formulations are applied, in their commercially available forms, by hand application to a backing by the whirler process. It is then dried by conventional methods after which a photographic negative is laid over the coating which is on a substrate and is exposed to ultraviolet light. After the desired exposure period, the negative is then removed and the portions of the coating underneath the transparent parts of the negative are rendered insoluble. When the negative is removed, the substrate with a particular color which has just been exposed is washed with a dilute ammonia solution to remove the portions of the applied coating which were not rendered insoluble by exposure to ultraviolet light.
Prior art formulations using nitrocellulose-based products, which are not water soluble, as a sealer coat, pose significant toxicological hazards to both person and property. After the nitrocellulose-based sealer coat is applied and dried, the only method for removing a portion or all of the sealer coat is by using a solvent, such as acetone. The disadvantages of the use of such a nitrocellulose-based sealer coat are numerous, including the cost and the health and environmental hazards inherent in a red label explosive vapor material such as nitrocellulose when used in a non-explosion proof and poorly ventilated color proofing shop environment.
Prior art processes used commercially in producing pre-press proofs consist of expensive mechanical equipment and involve the use of micropulverized pigmented material which is applied to a sensitized flexible film by hand or some mechanical means. Then the proper negative is placed over the flexible film which has the color applied and is exposed to ultraviolet light. After exposure the negative is removed and the applied color on the sensitized flexible film is developed. Successive sensitized films are used, each having its specific color. When the required number of flexible films are developed they are laminated after they are placed in register; however, the laminations cause a gloss and depth of image which is not achieved when the job is actually printed.